1. Field of the Invention
Exemplary embodiments of the invention relate to a method of fabricating a light guide plate and a backlight unit having the light guide plate, and more particularly, to a method of fabricating a light guide plate having a function of an optical sheet and a backlight having the light guide plate.
2. Description of the Related Art
Liquid crystal displays have been used in notebook personal computers, office automatic equipment, audio/video equipment, etc. because of advantages such as miniaturization, thin profile, and low power consumption.
The liquid crystal display includes a liquid crystal display module and a backlight unit. The backlight unit may be classified into an edge type backlight unit and a direct-under type backlight unit depending on a location of a light source.
The edge type backlight unit includes a light source unit, a light guide plate, a reflective plate, and an optical film.
The light source unit includes a light source such as at least one cold cathode fluorescent lamp (CCFL) and at lest one external electrode fluorescent lamp (EEFL), and a light source reflective plate on which the light source is positioned.
The light source produces light having a predetermined wavelength, for example, white light. The light source reflective plate reflects the light produced by the light source.
The light guide plate is positioned at one side of the light source unit so as to obtain uniform light. The light guide plate allows the light coming from the light source unit to travel toward the liquid crystal display module.
The light guide plate is made of a material having a critical angle of a predetermined value. The light guide plate is formed in a plate shape having an upper surface, a lower surface, and four sides.
Accordingly, in light passing through the side (i.e., an incident surface) of the light guide plate facing the light source unit, light having an azimuth angle smaller than the critical angle is emitted through the upper surface (i.e., an emitting surface) of the light guide plate, and light having an azimuth angle equal to or larger than the critical angle is totally reflected and diffused on the entire surface of the light guide plate.
The reflective plate is positioned on the lower surface of the light guide plate to reflect leakage light in an inside space of the light guide plate. The lower surface of the light guide plate may have a scattering pattern.
The optical film includes a diffuser sheet, a prism sheet, and a protective sheet. The diffuser sheet is positioned on the light guide plate and may include a lower diffuser sheet, a diffuser sheet support member, and an upper diffuser sheet.
The diffuser sheet diffuses light traveling through the light guide plate using beads distributed in the diffuser sheet.
The prism sheet is positioned on the diffuser sheet and includes a base film and prisms. The prism sheet focuses the light diffused by the diffuser sheet.
The protective sheet diffuses the light focused by the prism sheet to provide the diffused light to the liquid crystal display module.
In addition to the above-described configuration of the optical film, the optical film may use combinations of various sheets in order to diffuse and focus the light traveling through the light guide plate.
In the edge-type backlight unit, recent studies have been directed to decrease cost and make products thinner, for example, by removing the prism sheets and forming a prism pattern on the top surface of the light guide plate. But, in case that the light guide plate is formed by an injection molding method or a thermal press molding method according to a conventional guide light plate fabricating method, there are some problems. That is, it is difficult to make the light guide plate larger and obtain high yield because it is necessary to spend a long period for heating and cooling. Furthermore, there is a limit to enhancing an optical efficiency because it is impossible to form minute prism patterns due to a low pattern molding rate.
As related art directed to resolving the above-mentioned problems, Korean Patent laid-open publication No. 10-2007-0101951 discloses a method of fabricating a light guide plate which comprises patterning an ultraviolet curing resin using a roller having engraved patterns, and irradiating the patterned curing resin under ultraviolet ray to form a prism light guide plate.
It is only possible to produce the light guide plate having a thickness of blow 500 μm because a base member of the light guide is made of polyethylene terephthalate (PET). Accordingly, due to the thickness limitation of the base member, it is difficult to fabricate the light guide plate having a medium or large size.
Furthermore, it is difficult to form minute engraved patterns on a roller because the related art uses the roller made of a metal material. Although it is possible to form minute engraved patterns on the roller, another problem exist to deform the shape of the minute engraved patterns due to ultra violet ray which is used to cure the ultraviolet curing resin. Also, it is possible to generate faulty patterns because the patterned ultraviolet curing resin is maintained on the roller by an adhesive force between the ultraviolet curing resin and the roller.